Magnus conventions for building Ruby native extensions from a Rust core: define_class, TryConvert/IntoValue, exception mapping, GVL handling, TypedData GC integration, and rake-compiler distribution. Load when generating or reviewing Magnus Ruby bindings for a Rust library.
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---
name: magnus-bindings
description: "Magnus conventions for building Ruby native extensions from a Rust core: define_class, TryConvert/IntoValue, exception mapping, GVL handling, TypedData GC integration, and rake-compiler distribution. Load when generating or reviewing Magnus Ruby bindings for a Rust library."
---
- Use `magnus` crate for Ruby native extensions. Define classes with `magnus::define_class`.
- Map Rust types to Ruby using `TryConvert` and `IntoValue` traits. Return `Result<T, magnus::Error>`.
- Use `magnus::function!` macro for defining Ruby methods. Use `magnus::method!` for instance methods.
- Map Rust errors to specific Ruby exceptions: `magnus::Error::new(exception::runtime_error(), msg)`.
- Build with `rb_sys` crate and `magnus-build` for compilation. Use `rake-compiler` for gem distribution.
- Support Ruby 3.2+ with multiple ABI versions.
- Test bindings from Ruby using RSpec or Minitest. Test error handling and edge cases.
- Keep Ruby wrapper gem thin — business logic in Rust, Ruby provides idiomatic API.
- Handle Ruby's GVL (Global VM Lock) — release for CPU-intensive Rust code.
- Use `TypedData` for wrapping Rust structs as Ruby objects with proper GC integration.
- Anti-patterns: panics in Ruby methods, `unsafe` without `SAFETY` comments, manual memory management.
